linux-kernel - [PATCH v2 5/5] resctrl: Replace PM QoS logic with cpu_affinity_latency_qos

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Message-ID: <20250721124104.806120-6-quic_zhonhan@quicinc.com>
Date: Mon, 21 Jul 2025 20:41:04 +0800
From: Zhongqiu Han <quic_zhonhan@...cinc.com>
To: <rafael@...nel.org>, <lenb@...nel.org>, <pavel@...nel.org>,
        <tony.luck@...el.com>, <reinette.chatre@...el.com>,
        <Dave.Martin@....com>, <james.morse@....com>, <ulf.hansson@...aro.org>,
        <amit.kucheria@...aro.org>, <christian.loehle@....com>
CC: <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <quic_zhonhan@...cinc.com>
Subject: [PATCH v2 5/5] resctrl: Replace PM QoS logic with cpu_affinity_latency_qos_* helpers

Use cpu_affinity_latency_qos_* helpers to replace the dev_pm_qos_request
handling for CPU masks in pseudo-locking.

These helpers encapsulate latency QoS operations for a group of CPUs,
providing a consistent mechanism for request addition, removal, and error
handling. This improves code clarity and maintainability. As resctrlfs is
used on different platforms, a unified interface also makes it easier to
adapt to platform-specific CPU masks and latency QoS values.

The only functional change, and a beneficial one, is that when the latency
QoS value is updated for a CPU in the mask, the interface will actively
wake up that CPU to ensure the QoS setting takes effect immediately. This
helps enforce latency constraints in a timely manner on
performance-critical paths.

Signed-off-by: Zhongqiu Han <quic_zhonhan@...cinc.com>
---
 fs/resctrl/pseudo_lock.c | 51 +++-------------------------------------
 include/linux/resctrl.h  |  3 ++-
 2 files changed, 5 insertions(+), 49 deletions(-)

diff --git a/fs/resctrl/pseudo_lock.c b/fs/resctrl/pseudo_lock.c
index 87bbc2605de1..8be3ae804af9 100644
--- a/fs/resctrl/pseudo_lock.c
+++ b/fs/resctrl/pseudo_lock.c
@@ -108,25 +108,9 @@ static struct rdtgroup *region_find_by_minor(unsigned int minor)
 	return rdtgrp_match;
 }
 
-/**
- * struct pseudo_lock_pm_req - A power management QoS request list entry
- * @list:	Entry within the @pm_reqs list for a pseudo-locked region
- * @req:	PM QoS request
- */
-struct pseudo_lock_pm_req {
-	struct list_head list;
-	struct dev_pm_qos_request req;
-};
-
 static void pseudo_lock_cstates_relax(struct pseudo_lock_region *plr)
 {
-	struct pseudo_lock_pm_req *pm_req, *next;
-
-	list_for_each_entry_safe(pm_req, next, &plr->pm_reqs, list) {
-		dev_pm_qos_remove_request(&pm_req->req);
-		list_del(&pm_req->list);
-		kfree(pm_req);
-	}
+	cpu_affinity_latency_qos_remove(&plr->pm_reqs);
 }
 
 /**
@@ -149,36 +133,8 @@ static void pseudo_lock_cstates_relax(struct pseudo_lock_region *plr)
  */
 static int pseudo_lock_cstates_constrain(struct pseudo_lock_region *plr)
 {
-	struct pseudo_lock_pm_req *pm_req;
-	int cpu;
-	int ret;
-
-	for_each_cpu(cpu, &plr->d->hdr.cpu_mask) {
-		pm_req = kzalloc(sizeof(*pm_req), GFP_KERNEL);
-		if (!pm_req) {
-			rdt_last_cmd_puts("Failure to allocate memory for PM QoS\n");
-			ret = -ENOMEM;
-			goto out_err;
-		}
-		ret = dev_pm_qos_add_request(get_cpu_device(cpu),
-					     &pm_req->req,
-					     DEV_PM_QOS_RESUME_LATENCY,
-					     30);
-		if (ret < 0) {
-			rdt_last_cmd_printf("Failed to add latency req CPU%d\n",
-					    cpu);
-			kfree(pm_req);
-			ret = -1;
-			goto out_err;
-		}
-		list_add(&pm_req->list, &plr->pm_reqs);
-	}
-
-	return 0;
-
-out_err:
-	pseudo_lock_cstates_relax(plr);
-	return ret;
+	return cpu_affinity_latency_qos_add(&plr->pm_reqs, &plr->d->hdr.cpu_mask,
+					    30);
 }
 
 /**
@@ -275,7 +231,6 @@ static int pseudo_lock_init(struct rdtgroup *rdtgrp)
 		return -ENOMEM;
 
 	init_waitqueue_head(&plr->lock_thread_wq);
-	INIT_LIST_HEAD(&plr->pm_reqs);
 	rdtgrp->plr = plr;
 	return 0;
 }
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 6fb4894b8cfd..521fe70b0425 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -6,6 +6,7 @@
 #include <linux/kernel.h>
 #include <linux/list.h>
 #include <linux/pid.h>
+#include <linux/pm_qos.h>
 #include <linux/resctrl_types.h>
 
 #ifdef CONFIG_ARCH_HAS_CPU_RESCTRL
@@ -108,7 +109,7 @@ struct pseudo_lock_region {
 	void			*kmem;
 	unsigned int		minor;
 	struct dentry		*debugfs_dir;
-	struct list_head	pm_reqs;
+	struct cpu_affinity_qos_req	pm_reqs;
 };
 
 /**
-- 
2.43.0